Concluding our magical series from the TV star of the Olympics, with a brutally honest account of the years she spent battling with her weight — and a doomed love affair with an Army officer.

Clare in her racing years before she got together with Alice Arnold, who is now her civil partner

As I swung my leg over Respectable Jones, the horse I was riding in the 3.30 pm at Chepstow, I heard an ominous ripping sound coming from behind me.

I knew immediately what it was. I had put on so much weight that when I arrived at the racecourse on that October day in 1990, my thin leather boots strained as I battled to zip them up. Now, in full view of everyone who cared to look, my overly tight breeches had split down the back seam.

Fortunately I had not resorted to the old jockey's trick of taking my pants off that morning, saving a vital ounce or two to get down to the required starting weight for the race. But making it through this six-furlong sprint without exposing my underwear to the world would add considerably to the challenge of what lay ahead.

I was 19 and in my third year as a jockey. I had a good chance of winning the annual Ladies' Championship — one of the most prestigious prizes in the amateur racing calendar — and this last race of the season was the decider.

On the approach to the starting stalls, I anchored my horse's chestnut head towards the left-hand rail all the way. It meant that my bottom was pointing towards the middle of the course, away from the crowd, but there would be no room for such modesty during the race.

Even so, I was determined to cross the line first. Apart from winning one's weight in champagne — a considerable prize in my case — it offered a title which would look far more impressive on my list of certificates than Grade 2 Piano.

For the millionth time, I asked myself why I couldn't be tiny and featherweight like my rivals. As my own father, the champion racehorse trainer Ian Balding, had recently told a journalist: 'Clare is not really the right shape to be a jockey.'

It was the same point he had made, with even less diplomacy, one morning when I was 16. Though I started riding at about the same time as I learned to walk, this was the first time I had been allowed on a racehorse.

It was Miller's Tale, son of the legendary 1971 Derby winner Mill Reef, trained at our Hampshire stables.

'What were you doing' he snapped at me, as I pulled up at the end of a half-mile gallop. 'You looked like a sack of potatoes. You need to find a bit of muscle somewhere.'

He was right. Riding racehorses was about as similar to my kind of riding as flying is to driving, and I needed to improve my fitness dramatically. Or as Dad put it: 'You've got very porky. Lose it.'

Clare Balding with her partner, Alice Arnold, four years ago

Just how much I needed to lose became clear when, soon afterwards, he entered me for a flat race in Salisbury. I was 10st 5lb and he told me that I had to be 9st 10lb — more than half a stone lighter — in just ten days.

In the run-up to the race, I exercised three horses every morning. Every afternoon, I put on Dad's plastic sweat suit and went running, or cycled for miles on an exercise bike, listening to INXS on my Walkman all the while.

Next I would sit in the sauna for 40 minutes at a time. As for eating and drinking, I had half a cup of tea when I woke up, a slice of melon at breakfast with half a glass of orange juice and a slurp of coffee, salad for lunch, and a Lean Cuisine meal for supper.

It was hard work, and horribly boring. All I could talk about was how many pounds I had lost or needed to lose, and whether chicken or beef stroganoff was my favourite flavour Lean Cuisine.

I nearly fainted if I stood up too fast, and my mouth was dry with dehydration. I would collapse into bed by nine o'clock in the evening, hoping beyond hope that I would wake up two pounds lighter than I had gone to sleep. I stood on the scales at least six times a day. If I hadn't lost anything, I felt worthless. I trimmed my fingernails, shaved my legs and even had my hair cut short to try to save a few more ounces.

But the fact remained that I was a thick-thighed young woman whose bottom had a gravitational force all of its own. On the day of the race, I had to block my ears as an announcer declared over the public address system that Miss C. Balding would be carrying three pounds overweight.

'A few less pies next time, Clare!' shouted one punter as I came in second, but I was too elated to care. For the first time I had heard the roar from the grandstand as the crowd shouted us home, and it was such a thrill, such a total rush of adrenaline, that I became instantly hooked on racing.

From then on, I threw myself into my training and finally started to get the hang of it, my resulting weight loss bringing very varied rewards. That October, I took delivery of a brand-new Mini, my prize for winning the Amateur Riders' Championship at the end of that season, and the following summer I found myself a boyfriend …

We met at a party. An Army officer who was on leave before being deployed to the Falklands for three months, he had dark, floppy hair, olive skin and sparkling eyes, and was so damned handsome I could not believe he was talking to me. When he kissed me, my knees went trembly.

I assumed he would never bother to call, but he did — and we were inseparable until his leave ended.

From then on, we wrote to each other every day. It was the perfect relationship because it existed mainly in our heads, and neither of us had to change the course of our lives for each other.

But it was soon put to the test.

While he was away, my mother sent me to France to improve my language skills. There I discovered the joys of a warm baguette, with butter and strawberry jam. One mouthful after another of squidgy, comforting dough. So gorgeous, so cheap, so horrifically fattening.

My hips expanded, my breasts filled out, and I will never forget the look on the Army officer's face when he flew to Paris to see me. In the 12 weeks that we had been apart, I had gone from the strict starvation regime of a would-be champion amateur rider to a diet of one baguette a day.

Rubens may have appreciated my new-found curves, but the Army officer did not. Disappointment registered in his eyes when I went to meet him at Charles de Gaulle airport. 'You've been eating well,' he said as we embraced.

Clare Balding, BBC sport presenter carrying the Olympic Flame on the Torch Relay leg through the streets of Newbury

He obviously loved me more when I was thin, but the following year, as he was about to be sent to fight in the first Gulf War and I had won a place to study English at Newnham College, Cambridge, he asked me to marry him. The romantic in me was desperate to say yes, but the realist knew that it was the situation talking. I told him to ask me again when he came back.

Once again, we wrote to each other every day (we were good at that) and I busied myself with the distractions of my invigorating new world as a fresher.

In the first few weeks of term, I was also preparing for that championship race at Chepstow, which would see me testing my breeches beyond their limit.

Although I was desperate to win it, keeping my weight off was proving difficult. As I had discovered in Paris, starving and dehydrating my body for the summer's racing left me craving food in the off season, and my methods of fending off my appetite were increasingly unhealthy.

For a while I took a particularly revolting laxative — a pot of granules described as 'chocolate flavoured'. They could, more accurately, have been described as 'manure flavoured'. If I really felt I had over-indulged, I resorted to making myself sick.

I don't think I had an eating disorder, as such. It was just part of what anyone in a weight-related sport will do to beat the scales.

None of this seemed to be reducing my waistline much as the Ladies' Championship approached, and matters weren't helped by the excesses of Freshers' Week, with a different social event every night.

On the day, I knew I had to put my split breeches and all other distractions aside. And as the stalls opened, and Respectable Jones jumped straight into his stride, my mind went blank. I was, as they say, 'in the zone'.

More importantly, so was Respectable Jones. His pace did not weaken and, as his stride kept covering the ground with the same length and power, it began to sound musical: like the beat of a drum.

As we crossed the line, my body acknowledged our win, even if my brain couldn't take it in. I took my right hand off the reins and gave a low punch.

The walk back to the winners' enclosure was fabulous. All the punters who had backed us were cheering, and I loved being announced as 'the new Champion Lady Rider'.

But when I slid to the ground I was forced to turn my bottom towards my horse's body, so that no one would be able to take a photo. It was not an elegant dismount, and I had to ask my brother Andrew to walk directly behind me to preserve my modesty on the way to the weighing room.

Afterwards, I saw Lydia Pearce, the jockey I had beaten into second place, packing up her stuff. I knew how she must be feeling and I went over for a quiet word.

'At least you've got years to keep at it,' I said, trying to sound encouraging. 'Look at me — you don't get many years of race riding out of a body this big.' She laughed, and we both knew it was true.

Sure enough, that was the last year that I raced with any great intent. I ride only rarely now, and I am often asked if I miss it. It was a huge part of the first 20 years of my life, but these past 20 years have been dedicated to a broadcasting career that is stimulating, exciting and rewarding.

My personal life is equally fulfilling. Clare Balding. To order a copy for 15.99 (incl p&p) call 0843 382 0000. Clare Balding will be talking at the Henley Literary Festival on September 30 at 4pm. For tickets go to henleyliterary festival.co.uk or call 01189 724700.